The present invention relates to tissue culture systems and, more particularly, to a culture system capable of supporting human tumor stem cell colony growth in vitro.
Tumor stem cells are the cell renewal source of a neoplasm and also serve as the seeds of metastatic spread of cancer. Studies of transplantable tumors in animals indicate that tumor stem cell colony-forming assays, either in vivo or in vitro, can be used to study the biological properties of these cells and to delineate differences in individual sensitivity to a variety of chemotherapeutic agents, as described, for example, by M. Ogawa et al., Blood 41, 7 (1973) and by G. Steel et al., Cancer Res., 35, 1530 (1975). As an example of such a study, the development of an in vitro colony-forming assay for stem cells from transplantable mouse myeloma (a plasma cell neoplasm) permitted detailed analysis of the effects of anticancer drugs in vitro, and the assays are predictive of therapeutic responses even in animals with advanced mouse myeloma. Such an analysis is described by C. Park et al., J. Nat. Cancer Inst., 46, 411 (1971).
The ability to grow colonies from primary tumor cell explants in semisolid culture media has even greater potential application. Unfortunately, primary explantation of human tumors for colony formation in vitro has met with little success. One major problem has been the creation of an environment that gives tumor cells a selective advantage over normal cells. Several investigators have had occasional success in obtaining colony growth in soft agar with pediatric solid tumors, as described, for example, by R. McAllister et al., Pediatr. Res., 2, 356 (1968) and A. Altman et al., Cancer Res., 35, 1809 (1975). Most recently, the effect of drugs on human stem cell colonies has been studied with the use of xenografts established in nude mice and then culturing cells from these grafts in agar in diffusion chambers intrapertioneally implanted in mice that had been irradiated, as discussed by I. E. Smith et al., Br. J. Cancer, 34, 476 (1976). However, such multiple-step systems have not been clinically practical.
A standard colony-forming assay for human tumor stem cells could be used to determine the sensitivity of tumor cells from individual patients to drugs, irradiation, and other therapeutic modalities and would permit the demonstration of resistant clones of cells in previously treated patients. The development of such a colony-forming assay seems especially important in view of evidence described by P. Roper et al., Cancer Res., 36, 2182 (1976) indicating that the only valid measure of drug efficacy in killing an established culture of human lymphoma cells is the inhibition of their colony-forming capability.